It is a well-known aspect of polymer science that higher molecular weight polymers tend to have improved impact strengths than their lower molecular weight counterparts. This can have a significant impact on the end-use application of a polymer. MPMD containing polymers are known to suffer from difficulties in building molecular weight to a significant degree due to cyclisation of MPMD and its subsequent volatilization during the initial evaporation process of the polymerization cycle and end-capping of the polymer by the cyclized species (3-methylpiperidine), as disclosed in U.S patent application publication No. 2012/0165466 A1. Several efforts have been made in attempts to overcome this problem. However, these efforts do not seem sufficient to overcome this problem to a significant degree.
Also, very few MPMD based amorphous polyamides for use as molded articles have been disclosed. Due to the ever-present demand for new materials with differentiated properties, MPMD based copolymers provide a way to meet this demand.
A few references detail a significant number of amorphous polyamides based on hexamethylene diamine (“HMD”) which generally have a higher isophthalic acid content and a lesser amount of terephthalic acid. The ability of MPMD to disrupt crystallization of the polymer allows for a wider range of formulations to be produced (varying amounts of terephthalic and isophthalic acid content) while retaining the amorphous nature of the polymer. This will, in turn, affect the polymers thermal and mechanical properties allowing it to be differentiated from what is already available and previously described in the art. Thus, need continues to exist in the amorphous polyamide art for improved MPMD based amorphous polyamide compositions with differentiated properties.
Improved mechanical performance applies in many end-use applications of the polymer and in particular to the injection molding end-use for the polymer. Polymers employed in injection molding such as polyamides, copolyamides and their blended formulation are no exception to this fact of mechanical performance improvement, as is appreciated by the skilled person.
Furthermore, it is known that blending nylons with amorphous semi-aromatic polyamides (e.g., a semi-aromatic copolyamide of poly-hexamethyleneisophthalamide and polyhexamethyleneterephthalamide called “6I/6T”) can improve their retention of stiffness at temperatures above the glass transition temperature of the polyamide and up to about 100° C. However, due to the amorphous nature of the blend component, once above about 100° C., the stiffness is reduced to a level below that of the unblended nylon at the same temperature.
The mechanical performance of nylon (polyamide 6 and polyamide 66) is known to significantly drop-off above its glass transition temperatures (Tg). Off-setting this drop-off may be remedied by blending nylon with an amorphous partially aromatic polyamide, as described in U.S. Pat. No. 5,266,655. As a result, the mechanical performance is retained to a higher temperature above T5.
Similarly, high temperature resistant polyamides of semi-aromatic and semi-crystalline copolyamides, which also contain terephthalic acid, are known from European Patent No. 2,510,056B1. However, there is still room for improvement in this field.